For Immediate Release
August 20, 2002

Future designer polymers may be assembled like children's Lego toys using
modular polymer scaffolds programmed to attract building blocks of small
molecules. Weak and easily reversed chemical interactions would self-assemble
those molecules to form complex structures with predictable physical and
chemical properties.

Comparison of the strategies
to obtain copolymers: (A) traditional "living" polymerization
strategy and (B) the self-assembly strategy. Conventional strategy
(A) relies on the living polymerization of monomers, while the
self-assembly method is based on a universal backbone and the
controlled self-assembly of side-chains onto the backbone.

In the natural world, self-assembly techniques produce thousands of varied
life forms -- bacteria to human beings -- based on a relatively small
set of amino acids and nucleosides combined in different ways. By emulating
this natural system, polymer chemists at the Georgia Institute of Technology
hope to simplify the synthesis of new materials for light-emitting diodes,
optical storage materials, biosensors, drug-delivery materials and other
applications.

Already, the researchers have built copolymers that use independent chemical
bonding mechanisms -- also copied from the biological world -- to simultaneously
self-assemble two building-block functional groups through a simple "one-beaker"
process.

"The goal is to simplify the synthesis of designer polymers via
self-assembly using combinatorial chemistry," said Marcus
Weck, assistant professor in Georgia Tech's School
of Chemistry and Biochemistry. "Our group is taking design lessons
from Nature by incorporating into one system several of these weak interactions
to get a degree of complexity that is difficult to achieve otherwise.
We believe we now have the basic proof of principle to show that we will
be able to address this problem."

He explained the concept and described research progress August 18th
at the 224th national meeting of the American Chemical Society in Boston.

"We are developing a system based on a polymer that contains two
or three different basic units, each having a different recognition motive
for weak interactions," Weck explained. "We would ultimately
want to have a shelf with 30 or 40 polymer backbones. When someone needed
a new LED, for instance, we would just take our polymer backbones, synthesize
small molecules, then self-assemble them onto the polymer backbones. In
one simple step in a beaker on the lab bench, we could assemble the polymer
instead of taking two or three months to synthesize it with traditional
methods."

Using a multi-step self-assembly process based on weak hydrogen bonding
or metal coordination, Weck and his colleagues build -- and sometimes
take apart -- complex structures based on their polymer backbones. By
changing such variables as temperature, pH, ultraviolet light and solvent,
the researchers add and subtract the small functional groups that give
the structure its final properties.

Weck envisions a system of polymer scaffolds, each with slightly different
mechanical properties, such as strength, flexibility and hardness. Each
scaffold would have bonding sites engineered to attract specific small
molecules found in a collection of such functional structures. Placing
the scaffolds into a chemical bath containing one or more of these functional
molecules would initiate a self-assembly process that would add those
small molecules to the structure. Multiple steps could build complex structures
with the desired electronic, biological or optical properties.

With thousands of combinations possible, the process could quickly produce
new materials for testing by engineers seeking new materials with specific
properties. If those prototype materials failed to meet the need, reversing
a chemical bond would allow one of the small molecules to be removed and
replaced with an alternative for further study. Weck compares that to
the "plug-and-play" system used to connect computer peripherals.

"We could eliminate the elongated and complicated synthesis of polymers
and go directly to something that has the strength we want, but is reversible,"
he said. "We hope that our system will reduce the time required to
synthesize and test new chemical structures."

The researchers -- including Joel M. Pollino, Ludger P. Stubbs, Amy Meyers,
Joseph Carlise and Robert Kriegel -- have so far used hydrogen bonding
and metal coordination bonding together in a structure able to self-assemble
different molecules using the two independent bonding methods. In preliminary
testing, the different techniques appear compatible, with a molecule being
joined to one bonding system not affecting a molecule already joined using
the other system.

Potential chemical interference problems pose the greatest technological
hurdle to the new system, Weck notes. To build up complex structures using
self-assembly processes, he must be able to insert new molecules without
affecting molecules already part of the structure or disabling other bonding
systems. Natural systems do that well, but synthetic chemical processes
often suffer from unintended interactions.

"We have found some very nice systems that have very good properties
and will self-assemble and recognize our system very easily," he
said. "We now have a polymer backbone that has metal coordination
sites and hydrogen bonding sites. That means we can now add two small
molecules at a time. Each small molecule is programmed to fit its place
on the backbone, where it self-assembles and give us a new material."

The approach varies the strength of chemical interactions to gain the
right properties. In drug delivery systems, for instance, weak interactions
may be used to allow a therapeutic molecule to easily drop off the polymer
deliver molecule at the proper location in the body. But molecules used
in light-emitting diodes would require stronger bonds to hold the structures
together for the expected operating life of the device.

Because of the cost and complexity, Weck's system would likely be used
only for expensive specialty applications. Current commodity polymer uses
would continue to be produced using traditional polymerization techniques,
he said.

Weck's group has published papers on their approach in the journals Synthesis
and Organic Letters. The research has been sponsored by the Petroleum
Research Fund of the American Chemical Society and by a grant from the
3M Corporation.